Description of problem:
DetachDiskFromVmCommand throw exception while trying to detach LUN from VM

Version-Release number of selected component (if applicable):
is22

How reproducible:
100%

Steps to Reproduce:
1. Create ISCSI DC
2. Create a VM with RHEL
3. Stop VM
4. Create direct lun disk
5. Attach direct lun disk to VM
6. Start the VM and wait until it's operational (the VM should have 2 disks)
7. Attach another direct lun disk to the VM while it's up (the vm should have 3 disks)
8. Detach last lun disk from the vm while it's up

Actual results:
ERROR [org.ovirt.engine.core.bll.DetachDiskFromVmCommand] (ajp-/127.0.0.1:8702-8) [617d2218] Command org.ovirt.engine.core.bll.DetachDiskFromVmCommand throw exception: java.lang.ClassCastException: org.ovirt.engine.core.common.businessentities.LunDisk cannot be cast to org.ovirt.engine.core.common.businessentities.DiskImage
	at org.ovirt.engine.core.bll.DetachDiskFromVmCommand.executeVmCommand(DetachDiskFromVmCommand.java:94) [bll.jar:]
	at org.ovirt.engine.core.bll.VmCommand.executeCommand(VmCommand.java:87) [bll.jar:]
	at org.ovirt.engine.core.bll.CommandBase.executeWithoutTransaction(CommandBase.java:1131) [bll.jar:]
	at org.ovirt.engine.core.bll.CommandBase.executeActionInTransactionScope(CommandBase.java:1216) [bll.jar:]
	at org.ovirt.engine.core.bll.CommandBase.runInTransaction(CommandBase.java:1892) [bll.jar:]
	at org.ovirt.engine.core.utils.transaction.TransactionSupport.executeInNewTransaction(TransactionSupport.java:210) [utils.jar:]
	at org.ovirt.engine.core.utils.transaction.TransactionSupport.executeInRequired(TransactionSupport.java:149) [utils.jar:]
	at org.ovirt.engine.core.utils.transaction.TransactionSupport.executeInScope(TransactionSupport.java:118) [utils.jar:]
	at org.ovirt.engine.core.bll.CommandBase.execute(CommandBase.java:1236) [bll.jar:]
	at org.ovirt.engine.core.bll.CommandBase.executeAction(CommandBase.java:362) [bll.jar:]
	at org.ovirt.engine.core.bll.Backend.runAction(Backend.java:416) [bll.jar:]
	at org.ovirt.engine.core.bll.Backend.runActionImpl(Backend.java:395) [bll.jar:]
	at org.ovirt.engine.core.bll.Backend.RunAction(Backend.java:353) [bll.jar:]
	at sun.reflect.GeneratedMethodAccessor159.invoke(Unknown Source) [:1.7.0_45]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_45]
	at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_45]
	at org.jboss.as.ee.component.ManagedReferenceMethodInterceptorFactory$ManagedReferenceMethodInterceptor.processInvocation(ManagedReferenceMethodInterceptorFactory.java:72) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.WeavedInterceptor.processInvocation(WeavedInterceptor.java:53) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:58) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.InterceptorContext$Invocation.proceed(InterceptorContext.java:374) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.ovirt.engine.core.bll.interceptors.ThreadLocalSessionCleanerInterceptor.injectWebContextToThreadLocal(ThreadLocalSessionCleanerInterceptor.java:13) [bll.jar:]
	at sun.reflect.GeneratedMethodAccessor20.invoke(Unknown Source) [:1.7.0_45]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_45]
	at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_45]
	at org.jboss.as.ee.component.ManagedReferenceLifecycleMethodInterceptorFactory$ManagedReferenceLifecycleMethodInterceptor.processInvocation(ManagedReferenceLifecycleMethodInterceptorFactory.java:123) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.WeavedInterceptor.processInvocation(WeavedInterceptor.java:53) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:58) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.component.invocationmetrics.ExecutionTimeInterceptor.processInvocation(ExecutionTimeInterceptor.java:43) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.InitialInterceptor.processInvocation(InitialInterceptor.java:21) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.interceptors.ComponentDispatcherInterceptor.processInvocation(ComponentDispatcherInterceptor.java:53) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.component.singleton.SingletonComponentInstanceAssociationInterceptor.processInvocation(SingletonComponentInstanceAssociationInterceptor.java:52) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.tx.CMTTxInterceptor.invokeInNoTx(CMTTxInterceptor.java:259) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.as.ejb3.tx.CMTTxInterceptor.supports(CMTTxInterceptor.java:398) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.as.ejb3.tx.CMTTxInterceptor.processInvocation(CMTTxInterceptor.java:242) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.component.interceptors.CurrentInvocationContextInterceptor.processInvocation(CurrentInvocationContextInterceptor.java:41) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.component.interceptors.ShutDownInterceptorFactory$1.processInvocation(ShutDownInterceptorFactory.java:64) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ejb3.component.interceptors.LoggingInterceptor.processInvocation(LoggingInterceptor.java:59) [jboss-as-ejb3.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.NamespaceContextInterceptor.processInvocation(NamespaceContextInterceptor.java:50) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.TCCLInterceptor.processInvocation(TCCLInterceptor.java:45) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.ViewService$View.invoke(ViewService.java:165) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.as.ee.component.ViewDescription$1.processInvocation(ViewDescription.java:182) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61) [jboss-invocation.jar:1.1.2.Final-redhat-1]
	at org.jboss.as.ee.component.ProxyInvocationHandler.invoke(ProxyInvocationHandler.java:72) [jboss-as-ee.jar:7.3.0.Final-redhat-10]
	at org.ovirt.engine.core.common.interfaces.BackendLocal$$$view9.RunAction(Unknown Source) [common.jar:]
	at org.ovirt.engine.api.restapi.resource.BackendResource.doAction(BackendResource.java:242)
	at org.ovirt.engine.api.restapi.resource.BackendResource.performAction(BackendResource.java:158)
	at org.ovirt.engine.api.restapi.resource.BackendResource.performAction(BackendResource.java:149)
	at org.ovirt.engine.api.restapi.resource.BackendVmDisksResource.remove(BackendVmDisksResource.java:76)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_45]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) [rt.jar:1.7.0_45]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_45]
	at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_45]
	at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:167) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceMethod.invokeOnTarget(ResourceMethod.java:269) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceMethod.invoke(ResourceMethod.java:227) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceLocator.invokeOnTargetObject(ResourceLocator.java:159) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceLocator.invoke(ResourceLocator.java:107) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceLocator.invokeOnTargetObject(ResourceLocator.java:154) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.ResourceLocator.invoke(ResourceLocator.java:92) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.SynchronousDispatcher.getResponse(SynchronousDispatcher.java:542) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:524) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:126) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:208) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:50) [resteasy-jaxrs.jar:2.3.7.Final-redhat-2]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec.jar:1.0.2.Final-redhat-1]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:149)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:499)
	at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:169)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:145)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:97)
	at org.jboss.web.rewrite.RewriteValve.invoke(RewriteValve.java:466)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:102)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:336)
	at org.apache.coyote.ajp.AjpProcessor.process(AjpProcessor.java:488)
	at org.apache.coyote.ajp.AjpProtocol$AjpConnectionHandler.process(AjpProtocol.java:420)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:920)
	at java.lang.Thread.run(Thread.java:744) [rt.jar:1.7.0_45]

Expected results:
It'll succeed